In recent years, semiconductor devices of a leadless-package type such as an SON package (Small Outline Non-leaded package) type or a QFN package (Quad Flat Non-leaded package) type are widely used. Such a leadless-package semiconductor device is advantageous in terms of size and thickness reduction, because no external connection terminals project from the sealing resin covering the semiconductor element. An example of such a leadless-package semiconductor device is disclosed in JP-A-2016-18846.
The semiconductor device disclosed in the above document includes a semiconductor element, a lead frame, wires and a sealing resin. The lead frame is made of copper, for example. The lead frame includes a die pad and a plurality of lead parts. The die pad supports the semiconductor element. The lead parts are electrically connected to the semiconductor element with wires. The lead parts are the terminals for external connection and used for mounting the semiconductor device to a circuit board of an electronic device, for example. The sealing resin covers the semiconductor element.
Since the lead frame of the semiconductor device disclosed in the above document is made of copper, the lead frame may be oxidized in the atmosphere, so that an oxide film may be formed on the surface of the lead frame that is exposed from the sealing resin. Such a copper oxide film may have a poor solder wettability. Thus, when the semiconductor device is mounted to a circuit board of an electronic device with solder, the mounting strength may not be sufficient. Thus, such a semiconductor device has room for improvement in terms of the mounting strength to a circuit board, for example.